A liquid crystal display device according to the present invention has a thin thickness and is capable of displaying a black-and-white image suitable for a high level multiplexing drive. Accordingly, it can be utilized as a large-area display device of a dot matrix type or as a display of a wordprocessor, a personal computer or the like. In addition, it can be also utilized as a color display in such a display device.
Recently, field-effect type liquid crystal display devices having a twisted structure of liquid crystal molecules have been developed, in which the liquid crystal molecules are oriented with a twist angle of 180.degree. to 360.degree. to provide a wide range of high contrast (namely, a wide visual range) and to enable a high level multiplexing drive. One of such liquid crystal display devices is disclosed for example in EPO-0131216A3. In such a liquid crystal display device, the display color appears bluish or yellowish due to birefringence of the liquid crystal. Therefore, liquid crystal display devices for high level multiplexing drive, capable of representing the so-called black-and-white display hve been developed. Among some methods used in such display devices, the method of providing two liquid crystal panels one upon another for phase compensation (disclosed for example in U.S. Pat. No. 4,443,065) is considered to be the one enabling the background hue (the background color) to be most close to white.
The principle of this method will be briefly described. The hue observed due to birefringence of a liquid crystal is an interference color, which appears because a beam is elliptically polarized in a liquid crystal layer. Consequently, an achromatic color can be obtained by twisting back the once twisted beam. For this purpose, a liquid crystal panel having the same characteristics as a liquid crystal panel used for driving, is placed on the liquid crystal panel, so as to be used for achromatization.
However, such liquid crystal panels have a large number of pixels because they are suited for a high level multiplexing drive, and accordingly have a large display area. In addition, the interference color depends also on the thickness of a liquid crystal layer and consequently, strict control is required for attaining evenness of the thicknes of the liquid crystal and stable characteristics. As a result, the manufacturing efficiency is lowered and the manufacturing cost are high. Further, the entire body of the display device becomes thick because two liquid crystal cells are placed one upon another, which unfavorably causes a deviation of a display position or a change in contrast due to parallax (dependent on the observing direction).
On the other hand, in order adjust hue in a liquid crystal display device, the method of using a 1/4 wavelength plate (1/4.lambda. plate) or a phase plate is conventionally used (as disclosed for example in U.S. Pat. No. 4,232,948). However, although coloring and achromatization are simply regarded as being based on opposite theories, it is practically difficult to effect achromatization by circular polarization or using a 1/4 wavelength plate. Particularly, it is difficult to adjust optical characteristics because of varioous factors such as a darkened display, a lowered contrast or appearance of other interference color and if the liquid crystal layer does not have stable characteristics over a wide area, the quality of display is further lowered.